The present invention relates to a part of an exhaust duct for the outflow of a fluid, in particular for the outflow of the exhaust gases of an internal combustion engine.
The parts or segments of exhaust ducts fitted to motor vehicles are of the type comprising, in succession, at least one fluid transfer section and a section containing an acoustic attenuation unit called an exhaust silencer or muffler.
The acoustic attenuation means which are employed in exhaust silencers and have recourse principally to the phenomena of absorption, reflection and interference in their totality necessitate the provision of an independent section of the exhaust duct, in which section they are arranged and to which there are connected one or more transfer sections which permit the entry and exit of the exhaust gases. A silencer is traditionally made up of a cylindrical box of large diameter to which are connected the transfer sections, the diameter of which is much smaller and which essentially fulfil only a function of transferring the gases to be treated.
This design presents numerous disadvantages. By reason of its internal design, the box of the silencer forms, for example in its lower part, a reservoir for condensates and sludge which, in combination with the significant variations in temperature to which it is subjected, cause very considerable corrosion phenomena, for the most part ending in the destruction of the silencer, necessitating replacement of this component on the vehicle to which it is fitted.
Furthermore, the concentration of the acoustic attenuation means in a casing of very large diameter has the disadvantage of concentrating a significant mass of the exhaust duct at a particular point of the exhaust duct. This causes phenomena associated with imbalance, which prejudices the reliability of the exhaust duct, of the devices for fixing the exhaust duct to the vehicle and of its connection to the engine, and generates undesirable noises during use.
An exhaust duct part comprising a silencer of this kind requires numerous welding and/or crimping operations, in particular for closing the cylindrical casing of the silencer by two transverse end plates as well as for connecting the transfer sections. These operations are complex and costly operations and impair the high-speed production of exhaust ducts.
This known design of a part of an exhaust duct which comprises at least one large-dimension silencer likewise poses numerous problems with respect to its installation on a motor vehicle and its arrangement on the lower surface of the floor of the body of the vehicle. Increasing the interior comfort of vehicles has made it necessary to arrange numerous components on the lower part of the vehicle, and in particular the fuel tank, and this further increases the problems of installing the exhaust duct. The appearance of four-wheel drive vehicles with means for transmission to the rear wheels, which occupies a considerable space, has likewise aggravated these problems.
To remedy some of the disadvantages just mentioned, a proposal has already been made in FR-A-1,301,056 for an exhaust duct for the outflow of a fluid, in particular for the outflow of the exhaust gases of an internal combustion engine, of the type comprising a continuous external casing of substantially constant cross-section and containing at least one acoustic attenuation unit positioned longitudinally in the casing so as to delimit at least one fluid transfer section of a length determined in such a way that the transfer section participates in the acoustic attenuation function of the exhaust duct part, the attenuation unit comprising a casing of substantially circular cross-section which, together with the external casing, delimits at least one longitudinal peripheral channel for the passage of the fluid.
In this reference, it is however to be noted, on the one hand, that the surface of interaction between the fluid and the attenuation unit is reduced in that it is at the maximum equal to the circular cylindrical external peripheral surface of the casing of the attenuation unit and, on the other hand, that the active path of the gas stream is equal to the length of the casing.